The present invention relates to an electric rotating machine, in particular to the electric rotating machine, in which improvements are made on stator iron or steel sheets and on positioning of penetrating or through bolt holes thereof, in a small-sized electric rotating machine.
An electric motor is known as an electric apparatus for converting electric energy into mechanical energy. In the electric motor, in which an electric system and a mechanic system are combined, there are used a relative motion between magnetic field and conductors and the electromagnetic force caused between the magnetic field and current, and an attraction and a repulsion between those magnetism. As one sort of such the electric motors, there is known an electric rotating machine which performs a rotating movement, and is used a direct current (DC) motor, or an alternating current (AC) motor, etc.
The electric rotating machine, such as an AC servo motor, etc., comprises, as shown in FIG. 4, a stator including a stator core 101 and stator coils 102, a rotor 103, a frame 105, and end brackets 106 and 107, etc. The stator is constructed with the stator core 101, which is formed through caulking of laminated layers of stator steel sheets, or through fixing of them by means of laser beam welding, etc., and in gutter portions of this stator core 101 are provided the stator coils 102. The stator steel sheets are formed by punching a belt-like iron or steel sheet, for example, and it is common that the punching shape comprises a main body portion of functioning as a magnetic circuit and end portions, in a part of which are provided the through bolt holes for the purpose of fixing the stator onto the end brackets 106 and 107 thereof.
The rotor 103 has a rotating shaft 104, and is held between the end brackets 106 and 107 through shaft bearings 108 and 109. The shaft bearing 108 is protected by a bearing protection cover 133. The end bracket 106 at a load side has the through bolt holes and outer attachment bolt holes, wherein the stator is fixed by means of the through bolt holes and through bolts, while being fixed to an outside portion by means of the outer attachment bolt holes and outer attachment bolts. And, the shapes of parts which constructs the electric rotating machine are designed to be in the rotational symmetry as far as possible, therefore a circle and/or a square are/is preferable. Also, an outer shape of a flange member gives an effect upon the size of the electric rotating machine, therefore it is so determined to be equal to around an outer shape of a container. Further, there is provided an encoder 110 for performing the detection of position and velocity of the rotor.
In the conventional electric rotating machine, the stator steel sheet has the through bolt holes provided or formed at every corner of the main body thereof, however they are shifted so that the through bolts and the outer attachment bolts do not overlap each other. For example, though the outer shape of the end bracket is nearly in the shape of a square, the stator steel sheets is formed into a nearly rectangular or oblong shape, and the through bolts are provided at the every four corners thereof. Also, it was done that, while forming cutting portions of the square shape at the every four corners of the stator steel sheets, the through bold holes are provided or formed in one side portion of the cutting portion.
However, when forming the stator steel sheets in the rectangular or oblong shape, the rotational symmetry is broken, and therefore the magnetic property thereof is deteriorated. Also, when forming the cutting portions at the ever corners, since the side portion of the cutting portions where no such the through bolt hole is formed does not participate with nor contribute to the magnetic performance, an amount of use of the steel sheets comes up to be more than that being necessary, thereby causing a problem that the stator becomes heavy in the weight thereof. Also, there was caused a problem that the magnetic circuit is deteriorated in the symmetry thereof.
An object, according to the present invention, for dissolving such the problems in the conventional arts, is to provide an electric rotating machine, with which can be maintained the rotational symmetry of the stator steel sheets, as well as the symmetry of the magnetic circuit, without increasing the weight of the stator.
According to the present invention, there is provided an electric rotating machine comprising: a stator having a stator core being formed by accumulating and fixing a plurality of stator iron or steel sheets, and stator coils; a rotor having a rotation shaft being received within an inner periphery side of said stator; a frame for receiving said stator therein; and end brackets for holding the stator and the rotor therein and having through bolt holes, wherein said stator is fixed to said end brackets by through bolts, and the electric rotating machine is installable onto an outside by means of outer attachment bolts through outer attachment bolt holes which are formed in at least one of said end brackets, and said stator iron or steel sheets are in a shape being symmetric both sides and upside down with respect to an axis of symmetry, each having a main body portion functioning as a magnetic circuit and corner portions, in each of which a through bolt hole is formed, said through bolt holes are provided on said axis of symmetry and on a circumference around the rotation shaft of the rotor at an equal distance therebetween, and further a line connecting between the through bolt hole and the rotation shaft of the rotor is shifted from a line connecting between the outer attachment bolt hole and the rotation shaft of the rotor so that they defined a predetermined angle therebetween.
Also, in the electric rotating machine according to the present invention, wherein said main body portion is in a form, an outer periphery of which is a circle around the rotation shaft of the rotor.
And, in the electric rotating machine according to the present invention, wherein the predetermined angle lies within a range from 100 to 200.
Further, in the electric rotating machine according to the present invention, preferably said predetermined angle is symmetric at both sides of the line connecting between the through bolt hole and the rotation shaft of the rotor as an axis of symmetry.